January 17, 2010

Height-IQ-Gender interplay

Am J Psychol. 2009 Winter;122(4):527-36.

The role of height in the sex difference in intelligence.

Kanazawa S, Reyniers DJ.

Recent studies conclude that men on average have higher intelligence than women by 3-5 IQ points. However, the ultimate evolutionary question of why men should have evolved to have higher intelligence than women remains. We suggest that men may have slightly higher intelligence than women through 4 mechanisms: (1) assortative mating of intelligent men and beautiful women, (2) assortative mating of tall men and beautiful women, (3) an extrinsic correlation between height and intelligence produced by Mechanisms 1 and 2, and (4) a higher-than-expected offspring sex ratio (more sons) among tall (and hence intelligent) parents. Consistent with our suggestion, we show that men may have higher IQs than women because they are taller, and once we control for height women have slightly higher IQs than men.The correlation between height and IQ and the female advantage in intelligence persist even after we control for health as a measure of genetic quality, as well as physical attractiveness, age, race, education, and earnings. Height is also strongly associated with intelligence within each sex.

26 comments:

The creators of the very first IQ tests found that women on average scored higher than men. They felt that this couldn't be right. They noticed that women on average did best on the verbal elements of the test. So they adjusted the test, adding more mathematical and geometrical questions, until they had a test on which women and men scored the same on average.

All subsequent IQ tests have been calibrated in the same way - to give an average score of 100 in males and females within the population that is to be tested.

However - this is the crucial bit - males and females differ in the steepness of the bell curve of IQ distribution. There are more males than females at the extremes i.e. more male geniuses and more males with severe mental handicap.

So if an academic tests a bunch of his handiest subjects - university students - voila! Males score on average higher than females. (Sigh). Now they are trying to figure out why this should be, when they haven't even read a standard psychology textbook on IQ testing.

The higher proportion of males at the extremes of the spectrum points to the involvement of some genes on the X chromosome. (Males have only one X, so if there is a defective gene on that X, they don't have a chance of a functioning backup.) And if I recall rightly, some related genes have been found on the X. That doesn't mean that all genes related to intelligence are on the X. Some have been discovered elsewhere. There are probably many more yet to find.

IQ is a misleading measure. The more I know of the tests the less reliable they look to be neutral measures of real intelligence.

In fact, I understand that intelligence as such cannot be described linearly, as IQ scores do but is a highly multifaceted (even fractal) characteristic. If they included music and drawing, or socialization abilities, for instance, my IQ would surely drop dramatically... but in any case it would be just an arbitrary measure (not totally meaningless maybe but relative in any case).

Also it's highly doubtful that it's only defined by genetic parameters. Even if people seem to perform more or less consistently through their lifes (but a shot of cocaine, for instance may rise your stats by five points too, just because your attention and concentration is temporarily enhanced), there are many factors that condition early development and that are manifest via epigenetics and maybe related psychological matters. Traumatized people lose intelligence for example, nutrition is crucial in mental development and I'm pretty sure that internalized social expectations also play a major role.

Going out on a limb here, but what about estrogen? I once read a study that men given estrogen pills performed more poorly on cognitive tests than they had before they were given the estrogen pills. There are so many variables in studies between men and women, it is hard to control/account for them all. So how do estrogen levels at all ages, especially say age 10-20 vary between women who are taller or shorter, and lower and higher IQ? Just a thought.

Male intelligence being higher certainly fits with my life experience (although it may be due to living around people at the right tail of the bell curve as described above) but taller men being smarter than short men is not something I would have expected.

A human can lose up to 30 IQ points in a single week by reducing his sleep to 4 hours per night. This will recover when going to normal sleep (8 hours) however.

- Exercise. Humans drop in IQ if they do not use their brains anymore. The difference is up to 20 points between a human that stresses his brain all day and the very same human after 2 years relaxing and partying.

1. The bell curve shape for both genders states that there should be more male geniuses and more male retards. This not counting cultural bias that kept women in the kitchen for so long, unable to express their genius in a public manner, and even erased the existence of brilliant females in some cases.

2. Male and female parents are known known to distinctly imprint genes (some, not all) through all the genome. This kind of deactivation of the second gene, similar to what happens with the X chromosome in females, is very much new to science and poorly understood in its mechanisms. But it exists and even affects health (as the second gene can't act as backup, because it's epigenetically deactivated).

I can't find the relevant article right now for this single parent imprinting of the autosomal genome, but browsing for it I found other stuff that seems quite relevant to the discussion in general:

>>As you yourself pointed out there are more male geniuses than female ones so that would indicate that some of the intelligence genes are found on the Y-chromosome.

No. There is virtually nothing on the Y-chromosome except the instructions to make a male. That is why the Y is so much smaller than the X.

Research on intelligence-related genes on the X has been focussed on finding the deleterious mutations. But in theory the X is where we will also find the genes that give a boost to males at the top end. Picture a gene on the X that says "make some extra brain-chemical". If a male inherits it, he gets the full benefit (along with any side effects.) If his sister also inherits it, she has another X from her father, that might not have the "make extra" allele. In females one randomly-selected X is switched off in every cell. So she gets half the benefit (and half of any side effects.)

Of course if a girl gets the gene from both parents, then she gets the full benefit.

WARNING! This is theory. As far as I know, scientists haven't yet located a brain-chemical gene behaving this way. But this is the general pattern of genes on the X, for example colour-blindness. A boy gets the gene from his mother, and the trait appears in him. A girl will mainly be a carrier, unless she gets it from both parents.

If you want to know how far science has got in tracking genes for brain function, Google for SNPedia.

No. Worse. It's from the Department of Management, London School of Economics and Political Science. Translation: they have no relevant training.

Without reading the whole silly thing, I can't be sure, but it seems to be a follow-up to an other clueless paper from the same source or similar. I recall reading headlines "Men brighter than women", and tracing the paper to find that it was some academic with no background at all in psychology, who had tested a group of students from his university, blissfully unaware that the bell curve would predict his results.

@Average Joe: This article on the evolution of intelligence covers the ground: http://discovermagazine.com/2005/oct/sex

"The Y has been whittled down to genes governing a handful of functions, most entailing sperm production and other male-defining features. Meanwhile, the gene-rich X is the most intensely studied of the 23 chromosomes, largely because of its role in rendering men vulnerable to an estimated 300 genetic diseases and disorders associated with those mutations—from color blindness to muscular dystrophy to more than 200 brain disorders."

But "And while these differences seem to be largely to the female's advantage, permutations during the genetic recombination of the X chromosome may confer to a few men a substantial intellectual edge."

No. They both say the same thing. The Y-chromosome has shrunk down over the millennia into a coding segment for making males. Mother Nature (i.e. natural selection) has removed other coding from the Y, because it is too vulnerable there. If a mishap occurs on the Y, and there is an error in copying from father to son, there is no way for it to be removed by recombination in the next generation.

The recent article speculates that the rate of change over the millennia on the Y could have driven evolution on the rest the genome. Precisely how, the scientists don't know, but they are clearly going to have fun thinking about it.

This finding plays into a long-standing debate on the nature of mind and intelligence. The prevailing generalist theory, upon which the concept of IQ is based, holds that if people are smart in one area they tend to be smart in other areas, so if you are good in math you are also more likely to be good at literature and history.

(...)

Yet some cognitive abilities seem distinct from overall IQ, as happens when a person who is brilliant with numbers or music is tone-deaf socially or linguistically. Also, many specialized cognitive skills, including recognizing faces, appear to be localized to specialized brain regions. Such evidence supports a modularity hypothesis, in which the mind is like a Swiss Army knife -- a general-purpose tool with special-purpose devices.

"Our study provides the first evidence supporting the modularity hypothesis from a genetic perspective," said lead author Jia Liu, Professor of Cognitive Neuroscience at Beijing Normal University in China of the study published in the Jan. 7 issue of Current Biology. "That is, some cognitive abilities, like face recognition, are shaped by specialist genes rather than generalist genes."

To Jean, your explanation on the theory of the "make more" (brain chemical) does not make sense. Your use of probability isn't actually describing the general case of what you are trying to argue. However if that allele on each x chromosome were effectively averaged in its expression then that would support the idea of a steeper bell curve for girls.

"Why this stuff is getting published"... its psychology there standards are not very high.

And yes girls are now outperforming boys in school. Boys haver been neglected and left behind. I hope your insecurities do not make you take glee in this fact.

there is a whole bunch of features related to this complex that are not wuthin the scope of the articles or comments, interesting btw how these tests got calibrated (lol). i rili like many of the comments here, and since my eq is quitte fine you may consider that a compliment. i assume , no i am quitte convinced the basical premise that taller man would (especially in premonetarian society) marry more beautifull woman is ok. not only that, many western woman 'dream of' tall man.

the basic mechanism for that is mutual, woman look for safety (a male able to put up a strong defence), and many of the taller man stand a better chance in physically competing over them.

however... there is a huge distinction between matriarchal (or actually better and more precisely relict matriarchal (comp istarte. and stone age mother goddes centrism)) societys and patriarchal societys corellating with smart woman.

as such in my opinion the differences are empiric, yet artifical. and by changing the cultural reference sets, that is valuing treats like independence (and in our mutilated circumstance even agression)in woman it is easy to revrse the degrading trends.

however it is socially not that easy, since partnership choices especially in patriarchal society emphasisw looks.

this easily translates into that sturdier build and therefore (well its true mention eg. bigger noses) less attractive woman , fat/body mass is also a function of body length that may hamper a such development within our current aesthetics, don't easily find a more attractive partner (tall tho that is more relative(1), and or smart)

(1) it's a common complaint from really tall man it is not easy to find an attractive partner on so to say kissing height. when i meet tall woman looking for a partner i usually point them at the availability of rather numerous tall male candidates that tend to be still looking to.

Recent studies conclude that men on average have higher intelligence than women by 3-5 IQ points

Which studies exactly? The Lynn one was so flawed even a muppet like me could spot the huge skew up in his statistical work (by sampling the high performing college students they left out the norming effect of the female tendency to average and the high numbers of lower IQ males that take the male average down).

Well know that height and IQ have a link. It's related to genetic health and overal health and nutrition- if all of these are good the overall height and IQ will be higher.

More male morons too. Not being snitty. You should visit a special ed class, they are mainly male. A double copy of the X chromosome protects against a lot of IQ lowering defects (fragile X, dyslexia, for example).

Swings and roundabouts; more male morons and more male geniuses than women. The average is the same. The result from a high IQ school I investigated was an overal; 2:1 ratio for male 'geniuses' to female ones.

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